The present invention relates to a lithium flat battery comprising of a first housing part accommodating a first thin-layer electrode, a second housing part accommodating a second thin-layer electrode, and a separator located between the electrodes. Batteries of this type are known in particular from U.S. Pat. No. 5,558,957 and EP patent 862,227.
U.S. Pat. No. 5,558,957 describes a battery where the electrodes and the separator are placed inside a complex housing having a special frame and multi-layered electrical connector tabs. The complexity of the housing leads to a multitude of bonding connections in multiple layers and directions making stability and conductivity of this known cell questionable.
EP Patent 862,227 describes a cell of the kind mentioned above in which the design appears to be simpler but at the price that the electrical connector tabs of the electrodes pass through a film enclosing the complete housing, thus creating leakage problems. To avoid these leakage problems, this known proposition suggests a web-structure for the electrical tabs. This, however, has negative effects on the efficiency of the electrical tabs and their mechanical strength.
DE 3122 2658 describes a battery where the separator extends into an area between housing cup and housing lid of the battery with an additional seal placed between cup and lid. In this solution the cup is a very stable and stiff part in order to absorb forces during flanging of the cup borders over the cover. These flanging forces harmful for the separator are absorbed notably by a strengthening rim of the cup. For this reason the battery described is intentionally stiff and relatively heavy with an excessive amount of material and a complicated design.
U.S. Pat. No. 5,714,283 describes a pancake-like multi-layered battery where the separator extends into an area between the housing bottom an the housing cover but without having any bonding or sealing function. To the contrary, a special sealing compound and a fastening ring separately ensure these functions, thus generating a complex design.
U.S. Pat. No. 5,800,944 describes a button or coin cell battery where the separator extends between housing cup and housing lid in order to be wedged there during the flanging process. For this purpose the peripheral edge of the separator is folded or bent several times with the consequence that, during flanging, several peripheral areas of the separator are exposed to the necessary high flanging forces and possible damaging. Furthermore the geometry of the cell results in an essentially stiff body. The risk of damage during flanging is reduced by a sealing material placed at the flanging perimeter of the cell, possibly separating completely the separator from the sealing material. Altogether there is a complex design including, in particular, leakage caused by the flanging process.
The object of the present invention is to propose a flat battery
wherein the separator itself assumes a central supporting function,
the number of components is minimal combined in a simple assembly,
no leakage problems occur with optimal efficiency of the electrical connector tabs,
possible use in electronic cards, as for instance in so-called smart cards.
In order to meet these objects the invention suggests that the housing parts of the battery are built of electrically conductive, that the separator presents electrically insulating sealing and bonding material in the area where both housing parts are in contact with each other and that the housing parts are united by the sealing and bonding material on the separator thus forming through him a closed housing.
By this simple design, the housing parts can be realized as electrical tabs and the separator carries the sealant material for connecting the two housing parts and, at the same time, is the supporting and connecting element. Therefore the battery according to the invention is particularly suitable for installation in data-carrying systems having the thickness of plastic cards.
According to a preferred embodiment of the invention, the film building the battery housing as a metallic film. This realization eliminates the need for a separate film as in EP 862.227 and the related leakage problems.